A. Field of the Invention
The present invention is related to methods for decoloring sulfuric acid, and more particularly to a method for decoloring sulfuric acid having an organic reactive content by adding controlled amounts of potassium chlorate and hydrogen peroxide in a controlled environment.
B. Description of the Related Art
Normally, the sulfurous zinc concentrates used for generating SO2 for the production of concentrated sulfuric acid, are obtained in mines by flotation techniques. The sulfuric acid obtained contains organic reactives at the surface of the zinc sulfide particles.
The zinc concentrates are the main raw material of the metallic zinc production plants. The organic material contained in the zinc concentrates are partially burned at the roasting step at the zinc production plant, and the non burned fraction is distilled and dragged by the SO2 current to the plant where the SO2 is converted to H2SO4. The acid takes the organic material which gives the acid a yellow color.
The process for converting said SO2 into sulfuric acid comprises the steps of:
SO2 into SO3 conversion: the SO2 produced at the roasting step is converted into SO3 by reacting the SO2 with air in a catalyzed reactor with vanadium pentoxide in accordance with the following reaction:SO2(g)+O2(g)=SO3(g)
Adsorption in water: finally the SO3 reacts with water and H2SO4 is formed in accordance with the following reaction:SO3(g)+H2O=H2SO4
In the roasting step, some of the organic material that was incorporated to the mineral in the concentration step at the mine, is distilled, which are dragged together with the SO2 to the oxidation steps which produce small carbon particles that give a yellow color (80-100 APHA units) to the sulfuric acid when they are integrated to the same. Since the yellow color is not desirable for some of the clients, such situation created the necessity to develop a process for reducing the color of the sulfuric acid, without affecting the rest of the acid specifications which are concentration and impurity levels.
In order to decoloring sulfuric acid, there have been developed and patented various decoloring methods some of which will be described below:
U.S. Pat. No. 4,085,016 describes a method for the oxidation of organic material contained in concentrated sulfuric acid, comprising the steps of diverting a portion of a concentrated sulfuric acid stream, diluting the diverted stream with water to about 40-70% sulfuric acid concentration, passing the diluted stream through an electrolysis apparatus to oxidize some of the sulfuric acid to form a predetermined quantity of peroxosulfuric acids, and returning the diverted stream back to the main stream to oxidize the organic material and decolorize the main stream of concentrated sulfuric acid.
Japanese patent No JP58032003 describes a method for decoloring colored concentrated sulfuric acid in a short time, and to keep the acid to a required transparency without causing the clouding of the acid, by adding a proper amount of H2O2 to concentrated sulfuric acid colored with impurities under heating.
Japanese patent No. JP6219711 describes a method for denitrating and decoloring sulfuric acid comprising simultaneously adding sulfamic acid and an aqua hydrogen peroxide to the colored sulfuric acid containing NO2 or adding the sulfamic acid and subsequently the aqua hydrogen peroxide to the colored sulfuric acid.
Japanese patent JP2180704 describes a method for decoloring sulfuric acid derived from acid production methods, comprising adding hydrogen peroxide to the system at the final adsorption circuit and maintaining the circuit temperature over 70° C.
Japanese patent JP59078910 describes a process for decoloring sulfuric acid by contacting it with ozonized gaseous oxygen in a packed column structure.
Japanese patent JP60246207 claims a method for decoloring sulfuric acid by contacting an oxygen gas having a high specific concentration of oxygen with the colored sulfuric acid.
The method of the present invention achieves a high oxidant potential thus obtaining a crystalline sulfuric acid having a color index of les that 30 APHA unities.